1. Field of the Invention
The present invention relates to a humid air turbine, humid air turbine control system, and humid air turbine control method.
2. Description of the Related Art
A conventional humid air turbine obtains humid air by adding water to compressed air supplied from a compressor, uses the obtained humid air to recover thermal energy possessed by exhaust discharged from the turbine, and uses the recovered thermal energy to increase its output and efficiency. An invention disclosed in JP-A-2005-307861 provides means for exercising control to stabilize the amount of moisture in air without regard to load variations after the start of water addition in a humid air turbine.
When the rotation speed rises at turbine startup, the flow rate of air taken into the compressor and the vibration characteristic of a rotator generally vary. Therefore, system instability is more likely to result from disturbance than after full speed is attained. Particularly, if water addition begins during a rotation speed rise, the humid air turbine is disturbed. It is therefore preferred that water addition be started under partial load, which prevails after full speed is attained, in order to assure stability during turbine startup.
Meanwhile, if natural gas, kerosene, light oil, or other low nitrogen fuel is used, thermal NOx, which is generated when nitrogen in air is oxidized, accounts for the majority of NOx generated by a combustor. The amount of thermal NOx highly depends on temperature and increases with an increase in the temperature. Therefore, the basic idea of a low NOx combustion method is to reduce flame temperature. Premix combustion is known as a flame temperature reduction method that premixes fuel and air and burns the resulting mixture.
Even when combustion air is heated to a high temperature by a recuperator as in a humid air turbine, it is necessary to properly control the flame temperature for NOx reduction purposes while preventing the autoignition of fuel. Under such circumstances, a method disclosed in JP-A-2003-148734 can be effectively used to deliver many small-diameter coaxial jets of fuel and air into a combustion chamber.